In this article, the friction stir welding of dissimilar AA6061-T6/AA7075-T6 aluminum alloys was studied experimentally. The joining process was implemented with and without the addition of the TiO2 nanoparticles. To infer the resulting quality, tensile tests were carried out and the microstructure of the welded samples was investigated by the optical microscope. Furthermore, the samples were welded using gas tungsten arc welding (GTAW) to provide further comparisons with the FSW process. The ultimate tensile strength and maximum elongation increased by 12.3 and 12.5% respectively by adding TiO2 nanoparticles. Microstructure observation shows that equiaxed grains formed in the FSW process and no precipitation aging occurred in the melting zone -however, precipitation particles can be observed in the heat-affected zone. Coarser grains can be obtained by adding TiO2 nanoparticles, resulting in good dispersion at the stir zone and retarding the dynamic recrystallization (pinning the grain boundary movements). The sample welded by the GTAW process showed very weak strength compared to the samples welded by the friction stir welding process.
